Abstract

Members of the recent COVID -19 rapid response project on Test, Trace and Isolation interventions (TTI) for control of SARS CoV-2 in the UK, will present two strands of work. The first investigates the effectiveness of asymptomatic and symptomatic testing and tracing in reducing transmission in a population with high levels of immunity, for different testing frequencies, levels of uptake, contact levels and growth rates. We compare these policies to those akin to restrictions on social contacts ( reductions in workplace, school and other community settings). We find that perfect adherence to the current policy of asymptomatic testing twice a week on lateral flow tests, against a background of imperfect symptomatic isolation and PCR testing, yields a reduction in total number of infections by up to 20 , comparable to a reduction in the number of non-household contacts of 10%. The second piece of work describes an analysis to determine infectiousness by viral load. Test sensitivity varies by viral load at the time of testing, which itself varies strongly by infectious age. Infectiousness has been shown to vary by viral load, but we lack detail as to this exact relationship, which is key for fully representing the variation in viral load trajectories and implications for both test sensitivity and infectivity in models of TTI . Here we present a method to update existing analyses of the relationship between viral load and infectivity in contact tracing data, accounting for some identified biases.